On Monday, February 29, 2016 at 1:46:19 PM UTC-5, dpb wrote:
On 02/29/2016 11:24 AM, Don Y wrote:
...

I find it hard to believe that an architect (multiple architects?)
drafting plans for different homes (floor plans, construction techniques,
etc.) would be off by 1/2 inch "more than once".

So, did the builder (or, ONE of the builders in this subdivision)
get a deal on oddball doors? Did the carpenters and masons
screw up reading the plans? Have door dimensions changed over
the years? etc.
...

I venture none of the above...as another noted, doors are spec'ed by RO
and nominal dimensions; the various manufacturers have always had
slightly different precise measurements on prehung units.

I suspect if you'll measure you'll find the finished opening into which
the door fits is precisely 3-0 or whatever the nominal is and the door
slab itself is undersized to match the particular weather-stripping
system in use.

Built-in-place door frames and jambs generally will have a full-size
door slab and the opening will then be somewhat larger than nominal to fit.

Tract housing, even more "up-scale" than just starters 40-50 years ago
likely was using prehungs rather than custom-built even then although if
there's a significant time between the two and the earlier is '50s or
so, chances go up on custom framing.

--

Thank you for joining the RO discussion. I'm not sure why that isn't the
*only* thing being discussed. Trying to find a slab to just drop into an
existing jamb may end up being more work than just buying a pre-hung
door, with modern weather stripping, etc. At a minimum the options for a
slab that fits are going to be more limited than the vast selection of
per-hungs.